Scandium is extremely valuable as an additive for high-strength alloys and an electrode material for fuel cells. However, scandium has not yet been widely used due to small production quantity and high cost thereof.
Meanwhile, a trace amount of scandium is contained in nickel oxide ore such as laterite ore and limonite ore. However, nickel oxide ore has not been industrially used as a raw material for nickel for many years because the content level of nickel in nickel oxide ore is low. Consequently, very few studies also have been conducted for industrially recovering scandium from nickel oxide ore.
Nonetheless, in recent years, the HPAL process has been emerging for practical use in which nickel oxide ore is introduced into a pressure vessel along with sulfuric acid, and heated at a high temperature of 240 to 260° C. to allow solid-liquid separation into a nickel-containing leachate and a leach residue. A neutralizing agent is added to the leachate obtained from the HPAL process to separate impurities, and then a sulphidizing agent is added to recover nickel as nickel sulfide. Subsequently, this nickel sulfide is subjected to a known nickel refinement process to obtain electrolytic nickel and nickel salt compounds.
In the HPAL processes as described above, scandium contained in nickel oxide ore will be contained in a leachate along with nickel (see Patent Document 1). When a neutralizing agent is added to a leachate obtained from the HPAL process to separate impurities, and a sulphidizing agent is then added, nickel is recovered as nickel sulfide while scandium remains in the acidic solution after addition of the sulphidizing agent. In this way, nickel and scandium can effectively be separated by using the HPAL process.
Further, a method of recovering scandium from the above acidic solution has been proposed, the method comprising: allowing a chelating resin having an iminodiacetate salt as a functional group to adsorb scandium; separating impurities; and performing concentration (see Patent Documents 2 to 4).
In the meantime, a method of recovering scandium from nickel oxide ore by solvent extraction has also been proposed (see Patent Document 5). Patent Document 5 proposes a method of obtaining highly pure scandium oxide, the method comprising: adding an organic solvent to an aqueous phase scandium-containing solution to extract a scandium component into the organic solvent, the organic solvent comprising 2-ethylhexyl sulfonic acid-mono-2-ethylhexyl diluted with kerosene, and the aqueous phase scandium-containing solution containing one or more of at least iron, aluminum, calcium, yttrium, manganese, chromium and magnesium in addition to scandium; then adding an aqueous solution of hydrochloric acid in order to separate yttrium, iron, manganese, chromium, magnesium, aluminum and calcium extracted into the organic solvent along with scandium, and performing scrubbing to remove yttrium, iron, manganese, chromium, magnesium, aluminum and calcium: then adding an aqueous solution of NaOH to the organic solvent to transform scandium remained in the organic solvent into a slurry containing Sc(OH)3; filtering this to obtain Sc(OH)3, which is then dissolved in hydrochloric acid to obtain an aqueous solution of scandium chloride; adding oxalic acid to this to obtain a precipitate of scandium oxalate; filtering the precipitate to remove iron, manganese, chromium, magnesium, aluminum and calcium into a filtrate; and then performing calcination.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H03-173725
Patent Document 2: Japanese Unexamined Patent Application Publication No. H01-133920
Patent Document 3: Japanese Unexamined Patent Application Publication No. H09-176756
Patent Document 4: Japanese Unexamined Patent Application Publication No. H09-194211
Patent Document 5: Japanese Unexamined Patent Application Publication No. H09-291320